Differential signaling systems use cable pairs to carry a signal from a differential driver to a differential receiver. One cable carries the signal and the other cable carries an inverse of the signal. The receiver extracts the signal from the difference between the two signals. As a result, differential signaling systems are effective at rejecting noise in a signal because noise introduced on one cable will likely also be introduced on the other cable. Therefore, by focusing on the difference between the two signals, noise common to both cables is rejected. Additionally, differential signal systems are typically designed with redundant interfaces to limit the risk of complete failure (i.e. no data received) of the differential signaling system. In such cases, the redundant interface is enabled to replace the failed interface.
However, other problems may occur in a differential signaling system which do not cause a complete failure of the system but do degrade the quality of the signal received. For example, short or open circuits in only one cable and impedance changes along the transmission/reception path can lead to degradation of the differential interface. Since the system continues to function, albeit poorly or marginally, the problems are not detected and a redundant interface is not used. In addition, the source of these problems is often difficult to locate, especially since each distributed and lump impedance element along the transmission/reception path represents an opportunity for signal degradation.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a differential signaling system that can effectively detect and diagnose problems not resulting in complete failure of the system.